In recent years, a trend in which mounting is transferred from conventional surface mounting to area mounting due to progress of high density mounting technologies proceeds in the fields of electronic devices such as semiconductors and the like, and new packages such as BGA (ball grid ally), CSP (chip size package) and the like appear and are increasing. Accordingly, boards for interposers come to attract attentions more than before, and requirements to glass epoxy boards having a high heat resistance and a low thermal expansion are increased.
Under such circumstances, inorganic fillers, particularly spherical molten silicas are usually used in many cases in order to reduce usually a thermal expansion coefficient. Further, as environmental problems grow high, resins containing no halides are required and used as a flame retardant in combination with inorganic hydroxides including aluminum hydroxide in many cases (for example, patent documents 1 to 3).